This invention relates to a hydraulic brake system wherein a pump is activated to make available secondary pressurized fluid to a wheel brake in response to an input signal from an electronic control unit (ECU) to effect a decay-built sequence of fluid pressure supplied to a wheel brake and thereby prevent a potential wheel-lock situation during a first brake application and is subsequently activated to provide pressurized fluid to an accumulator that provides a brake booster with a hydraulic input to develop a force that acts on a master cylinder piston to effect a second brake application in responsive to an input from the ECU that indicates conditions under which the vehicle is operating may impair a safe operation.
In hydraulic brake systems for vehicles, it is common to use hydraulic fluid generated by a pump as a source of power to effect a brake application such as disclosed in U.S. Pat. No. 5,120,115. When a traction control function is added to this type hydraulic booster in a manner as disclosed in U.S. Pat. No. 4,815,793, the total length of the regulator and master cylinder may become an issue in a vehicle where under the hood space is limited. In order to reduce the overall length of this type hydraulic brake booster, it has been disclosed in U.S. Pat. Nos. 4,843,819 and 6,203,119 to use parallel boost pistons, which are connected to a master cylinder. However, when under the hood space is critical, a brake booster of the type disclosed in U.S. Pat. Nos. 4,514,981 and 6,142,584 have been used to control the supply of pressurized fluid to effect a brake application. These hydraulic brake boosters have satisfied many of the operational requirements of vehicle braking systems but space requirements and added cost associated with additional components limit acceptability by many customers.
The hydraulic brake booster may also be of a type as disclosed in U.S. Pat. Nos. 4,281,585; 4,539,892; 4,625,515 and 5,960,629 wherein an operational force for activating a master cylinder is derived by regulated pressurized hydraulic that acts on a piston to produce a force that correspondingly acts on a piston in a master cylinder to pressurized fluid used to effect a brake application.
It has been suggested that additional features, such as traction control and dynamic operational control can be implemented into a brake system through a modification of the inputs to an Electronic Control Unit (ECU) for a wheel lock control as some of the structural components, i.e. wheel speed sensors, build and decay valves and motor pump, necessary to provide such features are already available in a brake system.
A primary object of the present invention is to provide a brake system wherein a pump associated with a wheel lock system is utilized to supply an accumulator with pressurized fluid that is thereafter communicated as a hydraulic input force in response to an operator input applied to a brake pedal or under the control of a ECU to activate a brake booster for the development of a brake application to alleviate a sensed condition determined by the ECU that may impair safe operation of a vehicle.
According to this invention, the ECU receives inputs from various sensors associated with the operation of the vehicle and controls the operation of a pump for the wheel lock system to implement braking of the vehicle to attenuate the sensed condition. In this brake system, a brake booster is responsive to an operator brake input for providing a first input force to a master cylinder for pressurizing fluid therein. This pressurized fluid is thereafter supplied to wheel brakes in the brake system of a vehicle to effect a first brake application. The ECU receives among others signals, first input signals from sensors that indicate a speed of each wheel in the brake system of the vehicle. When a sensed speed indicates a condition where an imminent wheel lock may occur between the wheel and a surface the ECU supplies a decay valve associated with each wheel brake with a second input signal to open communication to a low pressure sump and allow pressurized fluid to be released from a wheel brake. When the condition is overcome, the ECU terminates the second input signal and the decay valve closes and supplies a third input signal to open a build valve associated with each wheel brake and allow secondary pressurized fluid from a pump to be supplied to the wheel brake for a continuance of said first brake application. When the ECU supplies the second input signal to the decay valve, the ECU simultaneously supplies a fourth input signal to the pump to begin the development of the secondary pressurized fluid and assure that the first brake application is completed in a manner desired by the operator as derived from the first input force. The ECU is also connected to a hydraulic input arrangement to control the timing and initiation of the communication of a hydraulic input force that is provided to the brake booster to effect a second brake application and alleviate a condition that may impair safe operation of a vehicle. The hydraulic input arrangement is characterized by an accumulator that is connected to receive and retain secondary pressurized fluid from the pump associated with the wheel lock feature in the brake system. The secondary pressurized fluid retained in the accumulator is selectively supplied to the brake booster as an actuation input to hydraulically activate the brake booster to effect the second brake application. A first sensor associated with the accumulator provides the ECU with an indication of the fluid pressure of the secondary pressurized fluid in the accumulator. When the fluid in the accumulator is below a predetermined value, the ECU directs a sixth input signal to activate the pump and supply the secondary pressurized fluid to the accumulator. In order to direct the secondary pressurized fluid to the accumulator, the ECU supplies a plurality of valves in the brakes system with input signals to either open or close communication to the pump. The plurality of valves includes: a first valve that is closed for preventing communication of pressurized fluid from the master cylinder to the pump means during that portion of the first brake application when pressurized fluid is supplied by the master cylinder to the wheel brakes and opened for allowing communication of secondary pressurized fluid from the pump to the wheel brakes when the fourth input signal is supplied to activate the pump; a second valve that is opened for allowing communication of the secondary pressurized fluid to the accumulator from the pump in response to the sixth input signal from the ECU and closed for preventing the communication of the secondary pressurized fluid from the pump to the accumulator during the communication of the fourth input signal to the pump when the pressurized secondary fluid is supplied to the build valve to the wheel brake; and a third valve responsive to the fourth input signal for preventing fluid from a source associated with the brake booster being communicated to the pump during communication of secondary pressurized fluid to the wheel brakes to assure that sufficient fluid is present in the brake booster system.
An advantage of this invention resides in a brake system wherein a pump is selectively controlled by an ECU to primarily function to supply secondary pressurized fluid to wheel brakes through a build valve and sustain a desired brake application and to function as a source for secondary pressurized fluid retained in an accumulator to provide the force to activate a actuator in response to the ECU.
A further advantage of this invention resides in a plurality of valves that are selectively activated by an ECU to provide an accumulator with secondary pressurized fluid that is utilized as a power source to activate a brake booster to effect a secondary brake application to attenuate conditions sensed by an ECU that may impair safe operation of a vehicle.